| Aluminum 7075 is a high strength precipitation hardenable aluminum-zinc-magnesium-copper alloy used extensively in aircraft and other highly stressed mobile structures where a high strength/weight ratio is desirable. Till now, this alloy has been joined by mechanical fastening as it is non-weldable by conventional welding methods. The cost of mechanical fastening of aircraft structures is becoming prohibitive and the new sophisticated technique of laser beam welding (LBW) with its high heat intensity and cooling rate should be studied for its potential in welding Al 7075.; With this aim, a comparative evaluation of gas tungsten arc (GTA) and laser welds of the alloy was done. Bead-on-plate welds with two different heat-inputs of each GTAW and LBW were carried out and later tested to compare their mechanical properties and arrive at some understanding of the welding process-property-microstructure relationship. It was seen that the laser welds resulted in deep and narrow welds with a narrow heat affected zone (HAZ). The grain coarsening in the HAZ of laser welds was less than that of GTA welds. Though the hardness (strength) of both GTA and laser welds was less than that of the parent material, the loss of hardness in the HAZ of LBW was much smaller. The tensile specimens of laser welds failed in the fusion zone whereas those of GTAW failed in the HAZ. In laser welds it is seen that the fusion zone is the weakest region in the entire weldment, while the strength of the HAZ is much higher.; Through this work, it was seen that laser beam welding does have a good potential for welding Al 7075. Optimization of weld parameters and properties, through further investigation, is essential to exploit this potential of LBW for commercial applications. (Abstract shortened by UMI.)... |
